What are the important factors that determine the selection of spring collet?

December 23, 2019

There are several factors to consider when deciding which spring collet is more effective. For a given lathe machining task, all of the following factors need to be considered when evaluating the selection of spring chuck or claw chuck.

1. Spindle load capacity

The maximum permissible weight of the lathe spindle is based on the carrying capacity. If the combined weight of chuck and workpiece is too large, the bearing may be overloaded. For those handling tasks where the danger exceeds the limit, this kind of danger may determine people's choice of workpiece fixture. A chuck with claws is usually heavier than a chuck with springs. Therefore, when it is necessary to control the weight, the chuck with spring is the appropriate choice.

2. Spindle speed

The spring collet is usually a better choice to rotate at a very high spindle speed for two main reasons:

One reason is related to the quality of the chuck. If the chuck and chuck are driven by the same spindle horsepower, the thicker chuck will take a long time to accelerate to the required speed, and the longer acceleration time will extend the working cycle and reduce the productivity.

Another reason is related to centrifugal force, because it increases with the square value of rotation speed, so in the case of high-speed cutting, this value is very important. For example, if the spindle speed doubles, the centrifugal force will be four times the original. If this force pulls the claw away from the center, the clamping force will often drop. However, if the spring chuck is used, the centrifugal force will not have a significant impact. Therefore, the clamping force is more stable in the whole processing speed range.

3. Processing operation

The spring collet exerts clamping force on the whole circumference of the part, rather than only on the selected contact area, so as to obtain good concentricity, which is particularly important for the secondary processing project. The secondary machining needs to consider the accuracy related to the primary machining, because the spring chuck has a strong ability of precise clamping. Even if the lathe chuck hydraulic chuck is used for multiple production and processing, the elastic chuck can also be used for re production and processing. The hydraulic chuck with the air indecisive lathe chuck can exceed the TIR (total reading value) repeated precision within the range of 0.0006 to 0.0012 feet, while the typical repeated precision of the elastic chuck is 0.0005 feet TIR or stronger. In order to further improve the secondary processing precision, the concentricity of the spring chuck can also be adjusted during the installation process.

4. Workpiece size

The spring collet is very suitable for work pieces less than 3 inches in diameter. The spring chuck limits the length of the workpiece. In particular, the spring chuck limits the axial (Z-axis) travel range of the machine tool, because its length is longer than the chuck. When the machining length of the workpiece almost needs the whole available travel of the machine tool, the chuck with claw may be used.

5. Processing batch size

Spring chucks are suitable for large and small batch machining tasks. In the case of small batch and multi task machining, the advantages of spring chuck are related to the product conversion time, and the replacement time of standard chuck is about 15-20 minutes. The jaw chuck for quick change only takes 1 minute, while the chuck for quick change of spring chuck only takes 15 to 20 seconds. When the products are changed frequently, the total time saved is considerable.

When the processing batch is large, the saving time related to clamping can be accumulated in the same way. The opening and closing time of spring chuck is less than that of claw chuck. By reducing the non cutting time from one workpiece to the next, the processing cycle time is reduced.

6. Workpiece size range

Part of the reason for the faster opening and closing of the spring collet is that it has a shorter drive stroke, and the size range of the workpiece applied by the spring collet is more limited than that of the collet.

In fact, the speed of the collet is elastic. If the size of the workpiece is the same, the speed of the spring collet will be faster. If the size of workpiece changes greatly, it may be necessary to use claw chuck to adapt to the processing of various sizes of workpiece.

7. Material type

For hot rolled steel, forgings, and molded parts, standard jaw chucks tend to work better because all of these parts have inherent diameter variations. On the other hand, some cold rolled materials usually have better dimensional consistency. Therefore, it is suitable to select the spring collet. However, the lack of a consistent diameter measurement does not necessarily hinder the use of the spring chuck, which can be set as a chuck with non-circular cross-section to keep the molding rod in the shape expected by the customer.

8. Secondary spindle

The milling CNC lathe equipped with secondary spindle bearing is often used for a variety of mass production and processing. In this application, the elastic collet can save more production and processing time. They can process all parts in a working cycle system. This kind of CNC lathe is often combined with bar feeder to realize unattended production and continuous processing of workpieces. In these applications, the chuck driving time saved may be very small for workpieces, but in the whole production process, the time saved for each workpiece is multiplied by the number of workpieces processed, and the accumulated time saved is considerable.

9. Chuck tool library

It is also important to consider the third option when choosing a suitable workpiece clamping device between the jaw chuck and the spring chuck. If permitted, it may be a cost-effective option to retain two types of fixtures, from one to the other.

From jaw chuck to spring collet, or vice versa, usually less than 20 minutes. The manual chuck can be kept on the machine tool in order to cope with the uncertainty of the range of parts. However, if the machine tool processes a large number of workpieces and several parts of the same size, the productivity of using the spring chuck will be improved, which greatly exceeds the productivity loss caused by the time required to replace the fixture.